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+/**
+ *    Copyright (C) 2022-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+#pragma once
+
+#include <queue>
+
+#include "mongo/db/operation_context.h"
+#include "mongo/db/service_context.h"
+#include "mongo/platform/mutex.h"
+#include "mongo/stdx/condition_variable.h"
+#include "mongo/util/concurrency/admission_context.h"
+#include "mongo/util/concurrency/mutex.h"
+#include "mongo/util/concurrency/ticket_queues.h"
+#include "mongo/util/concurrency/ticketholder.h"
+#include "mongo/util/hierarchical_acquisition.h"
+#include "mongo/util/time_support.h"
+
+namespace mongo {
+
+class Ticket;
+
+/**
+ * A ticketholder implementation that centralises all ticket acquisition/releases.  Waiters will get
+ * placed in a specific internal queue according to some logic.  Releasers will wake up a waiter
+ * from a group chosen according to some logic.
+ */
+class PriorityTicketHolder : public TicketHolderWithQueueingStats {
+public:
+    explicit PriorityTicketHolder(int numTickets,
+                                  int lowPriorityBypassThreshold,
+                                  ServiceContext* serviceContext);
+    ~PriorityTicketHolder() override{};
+
+    int available() const override final {
+        return _ticketsAvailable.load();
+    };
+
+    int queued() const override final {
+        return _enqueuedElements.loadRelaxed();
+    }
+
+    bool recordImmediateTicketStatistics() noexcept override final {
+        return true;
+    };
+
+    /**
+     * Number of times low priority operations are expedited for ticket admission over normal
+     * priority operations.
+     */
+    std::int64_t expedited() const {
+        return _expeditedLowPriorityAdmissions.loadRelaxed();
+    }
+
+    /**
+     * Returns the number of times the low priority queue is bypassed in favor of dequeuing from the
+     * normal priority queue when a ticket becomes available.
+     */
+    std::int64_t bypassed() const {
+        return _lowPriorityBypassCount.loadRelaxed();
+    };
+
+    void updateLowPriorityAdmissionBypassThreshold(const int& newBypassThreshold);
+
+private:
+    enum class QueueType : unsigned int {
+        kLowPriority = 0,
+        kNormalPriority = 1,
+        // Exclusively used for statistics tracking. This queue should never have any processes
+        // 'queued'.
+        kImmediatePriority = 2,
+        QueueTypeSize = 3
+    };
+
+    boost::optional<Ticket> _tryAcquireImpl(AdmissionContext* admCtx) override final;
+
+    boost::optional<Ticket> _waitForTicketUntilImpl(OperationContext* opCtx,
+                                                    AdmissionContext* admCtx,
+                                                    Date_t until,
+                                                    WaitMode waitMode) override final;
+
+    void _releaseToTicketPoolImpl(AdmissionContext* admCtx) noexcept override final;
+
+    void _resize(int newSize, int oldSize) noexcept override final;
+
+    QueueStats& _getQueueStatsToUse(const AdmissionContext* admCtx) noexcept override final;
+
+    void _appendImplStats(BSONObjBuilder& b) const override final;
+
+    bool _tryAcquireTicket();
+
+    /**
+     * Wakes up a waiting thread (if it exists) in order for it to attempt to obtain a ticket.
+     * Implementors MUST wake at least one waiting thread if at least one thread is pending to be
+     * woken between all the queues. In other words, attemptToDequeue on each non-empty Queue must
+     * be called until either it returns true at least once or has been called on all queues.
+     *
+     * Care must be taken to ensure that only CPU-bound work is performed here and it doesn't block.
+     *
+     * When called the following invariants will be held:
+     * - The number of items in each queue will not change during the execution
+     * - No other thread will proceed to wait during the execution of the method
+     */
+    void _dequeueWaitingThread(const ticket_queues::SharedLockGuard& sharedQueueLock);
+
+    /**
+     * Returns whether there are higher priority threads pending to get a ticket in front of the
+     * given queue type and not enough tickets for all of them.
+     */
+    bool _hasToWaitForHigherPriority(const ticket_queues::UniqueLockGuard& lk, QueueType queueType);
+
+    unsigned int _enumToInt(QueueType queueType) {
+        return static_cast<unsigned int>(queueType);
+    }
+    unsigned int _enumToInt(QueueType queueType) const {
+        return static_cast<unsigned int>(queueType);
+    }
+
+    ticket_queues::Queue& _getQueue(QueueType queueType) {
+        return _queues[_enumToInt(queueType)];
+    }
+
+
+    QueueType _getQueueType(const AdmissionContext* admCtx) {
+        auto priority = admCtx->getPriority();
+        switch (priority) {
+            case AdmissionContext::Priority::kLow:
+                return QueueType::kLowPriority;
+            case AdmissionContext::Priority::kNormal:
+                return QueueType::kNormalPriority;
+            case AdmissionContext::Priority::kImmediate:
+                return QueueType::kImmediatePriority;
+            default:
+                MONGO_UNREACHABLE;
+        }
+    }
+
+    ticket_queues::QueueMutex _queueMutex;
+    std::array<ticket_queues::Queue, static_cast<unsigned int>(QueueType::QueueTypeSize)> _queues;
+    std::array<QueueStats, static_cast<unsigned int>(QueueType::QueueTypeSize)> _stats;
+
+    /**
+     * Limits the number times the low priority queue is non-empty and bypassed in favor of the
+     * normal priority queue for the next ticket admission.
+     *
+     * Updates must be done under the ticket_queues::UniqueLockGuard.
+     */
+    int _lowPriorityBypassThreshold;
+
+    /**
+     * Counts the number of times normal operations are dequeued over operations queued in the low
+     * priority queue.
+     */
+    AtomicWord<std::uint64_t> _lowPriorityBypassCount{0};
+
+    /**
+     * Number of times ticket admission is expedited for low priority operations.
+     */
+    AtomicWord<std::int64_t> _expeditedLowPriorityAdmissions{0};
+    AtomicWord<int> _ticketsAvailable;
+    AtomicWord<int> _enqueuedElements;
+    ServiceContext* _serviceContext;
+};
+}  // namespace mongo